This application is based on Patent Application No. H11-292455 filed in Japan, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a measuring apparatus and measuring method, and specifically relates to a measuring apparatus and measuring method for measuring the three-dimensional shape of an object by scanning the object with light and receiving the light reflected from the object.
2. Description of the Related Art
The three-dimensional input apparatus of an optical system is an apparatus which outputs three-dimensional data or data based on such data representing the three-dimensional shape of an object based on a photographic image (slit image or spot image) from reflected light obtained by an image sensing element by projecting a slit light or spot light from a laser on the object.
The precision of the three-dimensional data is dependent on the signal strength of the photographic image formed on the image sensing element. When the signal strength is inappropriate, e.g., when the signal strength is too small and does not attain a value recognized as a reception signal, or when signal strength is too large so as to attain saturation, accurate three-dimensional data cannot be obtained.
One aspect of the image sensing element, for example, is that, if the image sensing conditions such as image sensing distance, exposure time, and circuit amplification and the like are constant, the signal strength at the center of the screen is approximately proportional to the intensity of the projected detection light. The signal strength of the image obtained by the image sensing element can be set at a suitable value by adjusting the intensity of the detection light.
Japanese Laid-Open Patent Application No. HEI 10-124646 discloses a method wherein a preliminary light is emitted at a specific intensity prior to three-dimensional measurement so as to set the image sensing conditions based on the signal intensity of the sensed slit image, and thereafter perform the main measurement. Japanese Laid-Open Patent Application No. HEI 7-23209 discloses a method wherein the amount of projection light is successively adjusted based on the measurement result of the total amount of light of a spot image formed on the photoreceptor surface of the image sensing element.
Disadvantages of the aforesaid conventional art are described below.
In the former method, for example, although an image of suitable signal strength may be obtained in the center of the screen, the signal strength at the edges of the screen may not necessarily be suitable.
In general, the light receiving lens produces different image plane illumination depending on the position within the image plane because such illumination is dependent on the optical characteristics of the lens, e.g., due to the existence of the cosine fourth law, and vignetting. In this case, xe2x80x9cdifference in image plane illuminationxe2x80x9d (in the presence of illumination irregularity) means that the value of the ultimately obtained signal differs depending on the position at which light enters due to the dependence on the optical characteristics of the light receiving lens and assuming light of equal intensity is projected to the image sensing system. When actually sensing light reflected by an object, the intensity of the received light will differ depending on the position within the screen in accordance with the shape and the like of the object (this allows the measurement of the shape of the object), but the image plane illumination invariably produces irregularities in the obtained signals assuming spot light of the same intensity enters the screen.
Specifically, when light passes through the light receiving lens and forms an image, the image plane illumination of the periphery of the light receiving area is reduced from the center area in accordance with the image plane illumination. That is, when a spot light is used as the detection light, the image plane illumination at the edges of the light receiving area may not be suitable even if the image plane illumination at the center area of the light receiving surface is suitable. Conversely, when image plane illumination is suitable at the edges of the light receiving surface, there may be saturation at the center area. Therefore, it may not be possible to obtain suitable signal strength over the entire screen.
In the latter method, the amount of received light is normally monitored, and the amount of light of the spot light is adjusted based on the monitor measurement result, so as to obtain a suitable signal strength at both the center area and the edges of the screen. However, since the amount of received light normally must be measured at high speed, a high-speed monitor element and high-speed feedback controls are required.
An object of the present invention is to eliminate the aforesaid disadvantages. Another object of the present invention is to provide suitable image illumination in all parts of the light receiving surface. Still another object of the present invention is to measure the shape of an object without requiring a high-speed photoreceptor element ore high-speed feedback controller.
These and other objects are attained by an apparatus for obtaining data relating to the three-dimensional shape of an object, said apparatus comprising: a controller for controlling a light beam; a scanning system for scanning an object by the controlled light beam; an image receiving system for receiving the light beam reflected from the object in a prescribed range; and a memory for storing data for correction of illumination irregularities corresponding to positions in said prescribed range, wherein the controller refers to the stored data according to the position where the reflected beam received by said image receiving system with referring to the stored data.
These objects of the present invention are attained by an apparatus for receiving the light reflected by an object, said apparatus comprising: a light source for emitting light; a deflecting mechanism for deflecting the emitted light to scan an object; a lens system for translate the light reflected by the object; a sensor for receiving the translated light; a memory for storing data dependent on an optical characteristics of the lens system; and a controller for controlling the emission of light in proportion to the deflection of light with referring to the data.
These objects of the present invention are attained by the aforesaid apparatus further comprising a range finder for measuring the distance from the apparatus to a point on the object, and wherein the controller refers the data corresponding to the measured distance.
The objects of the present invention are attained by a method for obtaining three-dimensional shape data of an object, said method comprising the steps of: emitting light; scanning an object with deflecting the emitted light in a predetermined range by a deflector; and receiving the light reflected from the object at light receiving positions along with the scanning of said scanning step, wherein the light emission of said emitting step is controlled in accordance with information representing a light receiving characteristics at each of the light receiving positions.
These objects of the present invention are attained by the aforesaid method further comprising:
a step of measuring the optical path length before aforesaid steps.
Image plane illumination ratio data D75, or other various forms of data may be used as data representing image plane illumination distribution. When image plane illumination ratio data D75 are used as image plane illumination distribution data, the spot light control means 61, for example, controls the intensity of the spot light and the image plane illumination ratio area so as to be constant.
The invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.